The present invention relates to a projecting direction control system for a vehicle headlamp, more specially to an art for preventing a misidentifying a posture variation caused by rolling on turning of the vehicle as a pith variation.
As an instrument for controlling the projecting direction of a vehicle headlamp such that the projecting direction thereof is corrected in response to variation in the vehicle posture, there is a known instrument for automatically adjusting the projecting direction of the headlamp (a so-called auto-leveling instrument) so that the projecting direction of the headlamp is held in a predetermined state even when the inclination of the vehicle changes. When applied to a headlamp system affording a large quantity of light with a discharge lamp as a light source, such an instrument is effective in improving safety as glare is prevented from being directed onto oncoming vehicles.
For example, as disclosed in JP-A-10-226271(Japanese Application Publication Number: Hei10-226271), the height value of a front-wheel axle portion is presumed or estimated from the information obtained by one height-detecting means (height sensor) provided in the rear-wheel axle portion of a vehicle by the use of a predetermined expression, and the pitch angle of the vehicle is then obtained so as to drive the reflecting mirror of a lighting device to negate the variation of the pitch angle whereby to perform correction control in order that the angle-to-ground of an optical axis of projection light is kept at a regular angle.
Further, as disclosed in JP-A-2000-233682 (Japanese Application Publication Number:2000-233682), JP-A-2001-058539 (Japanese Application Publication Number:2001-058539) and JP-A-2001-191842 (Japanese Application Publication Number:2001-191842), with respect to the driving condition of the vehicle, it is needed to distinguish between turning or slalom driving and stable driving at a constant speed that are different from each other.
However, in the conventional projecting direction control systems, it is feared that inappropriate projecting direction control may be performed in case that posture variation at the time of rolling due to the turning of a vehicle is misidentified as pitch variation.
For example, in the structuring (so-called one sensor system) of estimating the vehicle posture using the information obtained by one height detecting means (height sensor), the accurate driving posture of the vehicle cannot be captured when the output of the height sensor produced by rolling during turning motion is decided to be an output indicating the pitch variation, so that the correction of an optical axis of projection light cannot be made accurately as the behavior of the system becomes unstabilized. In other words, centrifugal force has to be taken into consideration when the turning motion of the vehicle is decided. Therefore, since the centrifugal force is proportional to the square of speed and inversely proportional to the slewing radius, information on the vehicle speed and the slewing radius is needed. However, the problem is that any system of detecting the slewing radius is not simple in configuration.